Telephone-exchange system.



T. G. MAHHN.

TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED MAY 29. I906.

RENEWED OLI. 25. I925.

Pawn M1 May 30,.1916.

T. G. MAR-UN TELEPHONE EXCHANGE SY' APPucAnpN FiLED MAY 29, I 906.

RENEWED ocr.

Patented May 30, 1916.

5 HEETSSHEEI 2 m w mw T. G. MARTIN.

TELEPHONE EXCHANGE SYSTEM.

APPLICATiON FILED MAY29,1906- RENEWED OCT. 25.1915- 1,1 85,522. Patented May 30, 1916.

5 SHEETSSHEET 3.

T. G. MARTIN.

TELEPHONE EXCHANGE SYSTEM.

APPLlCATION FILED MAY 29, I906 RENEWED 0C[. 25, 9!? 1,185,522. Pzmntvd May 30, 1916.

SHEEN-SHEET?- (ZWMMW Q .& ZZZ? zw aiyf .to increase the general clticiency and TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNOR.

BY MESNE ASSIGNMENTS, TO

FIRST TRUST AND SAVINGS BANK, TRUSTEE, OF CHICAGO. ILLINOIS.

TELEPHONE-EXCHANGE SYSTEM.

Application filed May 29, 1906, Serial No. 319,255. Renewed October 25, 1915.

ll) (177 whom it may concern.

lie it known that I. TALBOT G. MARTIN, a citizen of the United States of America, and resident of (.hicago, Cook county. Illinois, have invented a certain new and useful Improvement in Telephone-ldxchange Systems, of which the following is a specification.

My invention relates to telephone systems in general, but more particularly to automatic or semiautomatic telephone exchange system. and especially to systems in which two or more exchanges or central stations are connected by one or more trunk-lines. thereby atlording telephone service between subscribers of different exchanges.

Generally stated. the object of my invention is the provision of an improved and highly ellicient telcplmne exchange system.

Special objects of my invention are the provision of improved means for trunking both ways or in opposite directions over the same t unlcline: the provision of a two-way trunlelinc and means for automatically trunking both ways or in opposite directions over the saidtruulvline; the provision of means for automatically preventing seizure of a two-way trunk-line during the use thereof for autonnitically trunking in either direction: the provision of a line-relay adapted to serve as a part of a repeater for repeating switch operating impulses from one section of the line circuit to another. and also as a line-relay for controlling the operation of a trunleselecting switch mechanism; the provision of a two-way trunk-line havim; a line-relay adapted for use when the line is used for trunkingin either direction; the provision of an automatic telephone selectonswitch having line-relays adapted to serve also as a portion of a repeater; the provision of a two-way trunk-line provided at its opposite ends with means for rendering it busy when used for automatically trunking in either direction--that is to say, for establishing a guarding potential at both ends of the trunk-line when the same is used for automatically trunking in either direction; the provision of an improved two-Way trunk-line service for use in trunking or extending connections both ways or in opposite directions over one and the same line; and the provision of certain details and features of improvement and combinations tending service- Specification of Letters Patent.

Patented May 30. 1916.

Serial No. 57.868.

ability of a telephone exchange system of this particular character. i

To -e foregoing and other useful ends. my invention consists in matters hereinafter set forth and claimed.

Figures 1 and 2 together represent diagrammatically the calling subscriber of one central station (Fig. 1) connected with the called substati m of a second central s1ation (Fig. 2). Fig. 1 alone shows the calling substation X. the substation telephone line. a, first-select(n'-switch A. allotted to said line, and provided with suitable connections to the central battery B. As shown. the said first-selector is represented with the twoway trunking switch (Q7 of the calling exchange. Fig. 2 alone represents a called subscriber's station No. 2220. his telephone line and the first-selector A. allotted to said line. The two-way trunk switch l of the second central oiiice shown connected with the connectonswitch E, and the latter is shown connected with the called subscribers line. Said switch D is similar to the switch 0 of Fig. 1. Fig. 3 is a diagrammatic perspective. view of the first-selector A. Fig. l a

diagrammatic perspective view of my improved two-way trunk switch D. Fig. 5 is a similar view of the connector-switch E.

As thus illustrated. it will be understood that the subscribers stations may be. of any suitable or approved type. Substation as shown. has a rin jer 2 normally bridged across the line. Said substation is of the local battery type. in which the primary circuit that comprises the transmitter Z). the battery 4, and primary winding 3 of the in duction-coil 6 retained normally open by the switch-hook T at the springs 8 and 9. Said substation is providwl with a. tailing device for operating the switching apparatus at the central otlice. Said calling device may be of any desired type and is represented comprising a couple of push-but tons 10 and 11 for operating the springs 12 and 13 with respect to the ground post 14. Qaid springs 19. and 13, shown, normally engage the contact-points l5 and 1(3. respectively, but said connection is broken Whenever the said springs are forced onto the ground post 14. Said ground post is normally disconnected from ground. but Wher the switch-hook is raised a connection to ground is established through the'springs 17 and 18. The secondary circuit, of course, comprises the receiver 19 and a secondary winding 20,0f the induction coil 6. Said secondary circuit when the switch-hook is up, is bridged across the line, and at this time the rin er is cut oil". Said switch-hook 7 is provide with a. number of cam-arms 21, 22, 23 and 24 for controlling the substation circuits. The cam-arm 22, when the switchhook is down, engages the ringer circuit spring 25 for closing the ringer circuit, but when the switch-hook rises the said circuit is broken at the said point. There are two other springs 26 and 27 controlled through the medium of the said ringer spring :25. Said s rings are normally separated, but whent e switch-hook rises the said springs close into contact. The said springs 26 and 27 are-included in the secondary circuit for maintaining the said secondary circuit normally open. The primary circuit springs 8 and 9, previously described, are controlled by the cam-arm in such a manner that when the switch-hook is up the said springs are closed and when the-switch-hook is down they are open. The earn-arm 24 in turn controls the ground springs 17 and 18 through which the round post H is connected to ground lzastly, the cmnnrm 21 operates the rclease-springs 28, 29 and 30 in such a manner that as the switcluhooh (l8- scends the said springs are forced together to send simultuneous electric impulses to the central station apparatus over both sides of the subscribers line. The substation is also provided with a signaling button 31 for operating the spring 32 that normally engages the contact-mint 33 against the ground contact 34. y means of said signal ing button the connector ringer-relay is operated for signaling :1 called suhscriher in u u av that will he described.

The first-selector A is of the \veil-hnmvn and general type described in Patent No. 815.321, issued March 153 i906, to Keith, Erickson and Erickson. Said selector is provided with n snitch-shaft 35 for carry in! end movingihe line-wipers 3i) and 37 and the private-wiper 38. Sold shaft is up cmted vertically by the verticaluimgnet 39 is! raising the said wipers to any desired row or level of'tluline and private banks il and i1 rcs wctively, \Vhen raised the shaft is rotated hy'the r1 t:n'y-mu; n1v[ The releasehmgzuet l? is employed for renioring the switch after it has been operated. The wrticnl curl rotary line-relays ii uml s the l 'i lgcruboil-relny l6. lmvlifi-vicm'c Win i7. uml pi'ivotc-umguct 4. are uuxii' iaries for controlling said icrticul. roiury uml release magnets. The swirrluslmft has the usual cum 4! the longitudinal tccih 50 for rotating the shaft. and the circular teeth 51 for raising: it. A SWK'liltQii with said cir culai' teeth is the ciiziuuci 52 norinuliyooitupied by the shafiwrest The switch shaft is maintained in normal rotary position by the normal post 54- ;url the normal post-arm 55, against which post the said arm is retained by the spring; 56.

The connector E i cf the general type {itiscribed in Patent No. 815.1?6. issued March 13, 1906, to Keith, Erickson and Erickson.

In construction it is similar to the firstselector, althou h the circuits are quite dissimilar. Ssh connector is eiso provided with a switch-shaft 57 and Wipers 58, 59 and 80 to which are allotted the iine and private banks 61 and 6:2 .resy There is also a use-W1; '33. the long teeth 54; circular teeth 65, shaft-rest ("iii normal post 67, normal postnrm and the ccil-spring 69. Furthermore, there are the vertical magnet the rotary magnet TL and the reieuse zus nce and is eahiliiion the auxiliary vertical aiui'roterv iiue I'PiaQ-"S '13 and 74?, the-vertical and. rotary hackbridge-relays 75 and 76, :i1id,,ihe private magnet 77. The connector has a special luy known as the rin er-reiey it? for con meeting the ringer genezutcr 2'? across ihe culled subscrihers iine Wile-Z5 a connection established.

The nicrhanism ii-f the two-way trunking switch is the same that i' the iii'fii-fibridgemut-oli rehiy it hut the vertical magnet Sil the retainmagnet 8%, and the release-magnet Mgeiher with iii-iwivute umgrnet 83 the u cui :ziul rotary lino lays 84- unai respcciivei r run? {he inch release-reiuy 8i? perform Yew same oilice ascribe-.1 to the mini 1' in the firs selector" i ii there is in the rpm-Minn or uii'l rein. magnets wiil he et forth. Among the niurh'eii features oi my improved tori-Way trunk svitch are ihc verticui and rotor}; switching relays ii? and respectively. Norumllv us in the firshso ccior, the iclensw link 81? int-she the pin upon ihcih uiiie dog 9!, wherein; the re i'uctinpf'spriug 9&5 of the relcuseuumanure il ri r' iZ- his Hiiif, switch F in first position, niih the escupe- 'nenbfingzcy 34 ehind the imwr rem-om t 'escupeuicubtooth i l and with he lug 96 f the side switch ZH'Z'E! 7 resting: against a section 98 of the switch mm switch. of roui'schis nimfoil The points i :sism [he iamb c dog engages ill." llil; iill aha: pivoted to the .siir s"'iivh :ii ihe mm? iii'i. cvi (lent .hru that when the sh, strikes t e switch i'rzuuc 3 iihs .-.n in i i 'w max-r the r-aiilc vwitch on ivrthcr, um! double (log 91 will thus reach the limit oi it; Stroke. The :uijusinu'nt is such that non Ii1tlli--l1ll21l is, when the side switch is in first position, as llfi n in i i----- ;hi*

rturiinui il noi. in ulilc springs 103 and 11.11 are retained in engage nientbecause thc releasedink cannot he retracted any farther hy the retracting-- spring 92 after the lu; i strikes the frame 118; hut when the releahelinlt W is; withdrawn from the lug 110 the retra ting spring 92 carries the link as hack a little farther. whcreliy the springs 11 and 101 separate, and the said spring 1021 then cu gages the spring 10:1 This: is a new feature. It will he noticed that the spring 1 con trolled hy the link #49 through the medium of the arm lot The controlling: of the spring 193 is not necessarily limited to the method herein shown. Fartheruiorc. it is not necessary that the arm 1013 he perinaneatly attached to the link 85 it will he understood that while the douhle do; 511 is latched hy the release-link 81) the releasearmature 93 i drawn slightly toward the core of the rclea eauagnet 82; hut when the release-link is disengaged. a described. the rctractingrspring 51:! carries the release-armature 3 hack as far as it will go against any suitalilc stop that may he provided for said armature. it in the firstelector the ielease-arinatore retractiire-spring$ 2 (while the double do; is latched ll the l'(ltli. t link 8 retains the dolls 1t"? and 11) away from the shaft: hut when the (iUilllli do; is released hy the \ertical arm i the double dog retractirig-spring di'an the raid dog's toward the shaft in nch a manner that the dog 101', by engaging the circular teeth 1H prevents the shaft from falling when raised by the vertical pawl 111 upon the end of the vertical arm 10!). as the \ertical magnet M energized. 'hen the rotary magnet 81 is energized the rotar varinatnrc 11; is: attracteih and among other things that follow the shaft 11-? is rotated liy thc pawl 111 of the rotary aria 115' When the said rotary pawl engage the longitudinal tcclh 1113 the rotary arniaturcdingcr 117 at the same time depre ses the private armature 11* and also the interrupter-ling'cr 11 separate the interrupter-s irings 1'20 and 121 to destroy the energizing circuit through the r tary magnet "it as will he de cribed. The inter ruptcr is represented hy the interrupteriinger 11 and the springs 11") and 1:31. When the shaft is rotated the rotary do 10H engages the longitudinal teeth 111') and locks the shaft against hacliward rotation hy the tension of the shaft coil-sprin;1 122.

The operation is as follows: 'hen the Selcctor A is operated to connect ith the twoway trunk SWiU'l) the vertical switching relay $7" of the said switch C is energized through the private wiper 38 of the calling first-selector when the side switch of the said tirst-f-clector passes to third position. The said switching relay then causes the rotary switching relay SS topnll up. in the interval between the pullin' g up of the said vertical switching relay 87 and the pulling up of the rotary switching relay i851" a ground impulse is sent to the vertical trnnlc conductor 1:33 through a circuit that comprisc: a normally closed switch-point con iolhd hy the staid rotary switching relay Said impulse i c mparatively short, for ianncdiatciy a ftcr the \ertical switching: relay pu ls up the estahlished ground circuit is cut oil by the rotary switching: relay when the said relay opens up the said normally closed switch-point. This preliminary in1- pulse to the said trunk-conductor 123 operates the vertical line-relay 8101 the two-way trunk switch I). so that the vertical magnet 80 a caused to give a slight kick without rai ing, the shaft of the switch l). but snll icicnt to tlishzdge the release-link 89 from the douhle dog 91 and permit the springs 103 and 103 to come into contact after the said spring 10 1 leaves the spring 101. As a re salt the trunk-release-con luctor tilthat leads to the selector-bani of the second exchange i gr unded. 'lherefore. the seiz d trunleline is protected from ecizurc at hoth cxchanucs-at the second exchange, as just described. and at the lirst exchange when the si l Mvitcli \v hcr 1 50 of the first-selector A cne'ae'cs with the groundcd contact l-Ti thclcoi.

in detail the sitcliiii;3 operations are as foll ws: When the snhscri at the substation X wishes to call the auhscriher at subs a t-iou #1322) he presses the vertical and rotary huttons 1H and 11 twice and once, twice and once. twice and once, and ten times and once, rcsl'iectively. hen the button 10 is pre sed twice for the lirst time it energizes the vertical linca'clav 11 of the iirst-schator A range. f aid relay in turn energized the vertical magnet l! tnicc and as a result the shaft 1.") is raised two teps The i-nergizing' circuit for the vertira lincaclay H is from ground (1 to the substation ground thcn c through the ground springs 13 and 17 to the conduct rs 1 and 13 to the ground post 11, thence t the spring 12. verlical linc-conductor 134. side switch wiper 121.3. contact point 1Jll5 conductor 13f; yerti cal liuc relav -11. hriilgewntaiii-relay springs l 1318 and 135i to the battery-lead 110. thence through haticry B to ground (1. The vertil-a1 linc'rclay upon attracting its armature 111 forces the sprin 142 onto the ground spring 11 The vertical magnet 39 receives current through the following circuit: from ground (1 through the springs 14-3 and 142 to thc coinlnctor H1. private springs 1 15 and 1111 to the vertical magnet 39, thence to the hattm-v-lczul l1) and through battery H to ground (1. The vertical magnet 39 upon attractin, the verti'al armature 147 twicc through the medium of the vertical arni 118 causes the vertical pawl 149 to en- ;rage the circular teeth 51 and to rai e the shaft 350110 siep at a. mime. At th 1 first step of the vertical arm 148 the release-link 1.50 is drawn by the L-shaped ieec 151. frcm the dog lug 152 of ihe deuiile dog 153, so that the vertical dog L54 engages the circular teeth 51 to held the shaft in the first elevated pcsitiim. The shaft having been raised time steps the line and private wipers are raisedtc a level apposite the first con tact of the second level of their respective banks, and are in readiness to be rotated into engcgement with the contacts of said banks.

When the subscriber presses the reterjbuvfion 11 the rotary line-reiay 45 '01? the.

"armature 1 so that the privatekwiper 38 engages the first selector is energized in turn and aim relay then ran es the private magnefiB'ito be magnetized fcr operating the 'side' The energizing circuit for the rotary line-relay 45 may be traced from the sub simian. grmmcl G tcthe grcimri post. 14=,

mhcnce to thc rcmry iicc-ccndactcr 155, side 1' h wiper i516 wntacvpcint 157, conduclcr 1. 38, rotary line-relay 45, bridge-cutoffrelay springs 15%).. 1'38 and 13%) t0 the battery land 14 and thnmgh ltvattery B to ground (i. The rm" 1'}; lincrclaiy 4.3 then attracts its :mnctm i3 3 and thcr 0v prcsrcs the spring iii-l (min the gmcmi epring: H3. The ciao tri': current will then flow from grcnnd (i Lhi'uugh thc springs 1- 13 and 161., conductors i132 and 1133 w the primbc magnet 48, fihencc 4 the) battery-lend Hi) and through buticry .3 in. gmund i 5 .imi'ng tllai the first nine contacts cf JOINl level of th private bank 41 are t :mil, thcrcfm-e, that. the first nine Marks cf? Uh? 5c 1;. iii. cf the. line-hank J whcr: the private magneti5 1 0pm its armature causis the sidc h H to pa in 9004 position an ci1crining circuit is cstalumhcd through the m tar; mn 'nvt -1 2 that wili ("M150 the latter t0 rotate the sha it .il'lifi s At the very first 10 thv private wipe; 8 meets a guarding mtvnlial ;:i th first, contact cf the SiUUlid lcvc of {he privutc bank 4i, so that the private magnet ic rciiucrgr ed for locking {hi1 side which in iLIOiH/l position until thc mica-y magnet 3-2 his carried the Wipers past all busy trnulclim-xs. The private mag? in"; upon hccmning: encrgizcd, described, nth-11 st: lhc privatinilnaturc 164, whereby the escnpunwnt{with i043 (:lQlIS the escapewennfinger 1(34'. and the rc'crectirig-spring Hi7 advances ihc :Mi!ptll'ltilt-fillgbf U36 ga ner the upper rem-must BSCRPQlllfiflt-ilfi il lim. Whr-n ihc pl'irnic m'nmiure I'cilillis in manual pm-itiun the. 050;;pemcnbiinger i rlrms' in turn the l.-.'0h 1W4 anal thc lug H :11 the inner .;i the iiizguz liiii strikes the. 4.1: 49 illlll retains the said cscapcnwnt-finmntimmlly :ulvzuu-us ihc Sill? switch from,

cncposition to another during the. call. When the side switch passes to second position the side switch wiper 172 engages the grounded contact 173, whereby an energizing circuit for fihc rotary magnet 42 is established. The current in this circuit passes from ground G to the contact-point 173, thence to the side switch wiper 172, conductor 17% to one of the coils of the rotary mrlignet 452, thence threugh the springs 175 an 1'26 and through the other coil of the totary magnet to the battery-leed 140 and rhrcugh battery B ,m ground G. The reliary magma. upo'n attrwrizingthc rotary 7 rotates the shaft, 35 one step herbal-y B threugi; an occupying switch and hank multipling conductors to the first con.-

tact of the second levelv of the, privme bank 41, thence t-c'the privatc wiper'38, ccnductcr 1?8,'huck-releasc-re1ay 4:7, conductor 179 to the side switch wiper 130, thence kc the con- Ea --puint 3,80, ccnciucizcrs 131 and 163 to the p; are ma gmt i8, thcnce t0 the baircry -iccd 1.40 and through battery B to grccnd G. The private. magnet then attracts its armature U35. and locks the escapement-finger 266 behind the tooth 1.82 This, of ccurse, occurs before the can] 49 leaves the lug 169. The side switch being thus locked in second pqsitiun thc rotary magnet 42 is cncrgizcd intermittently long as the private wipcr 3h finds busy ccntact-puints along thecccomi lcvci of ihe private: bank 11. As a rcsult thrmmryarmature 37 7 is attracted step by step :mlii the wipers are carried intc engagement with 'lcnih trunk'lincof the. second lcve which, stated. the only truni -l1|ne on said lr-vel that is idic.

Al; the. instant that the private wiper 38 leaves the last busy ccntsct the energizing circuit through the private magnet -18 is rlcstrcycrl and the side switch H pasacs to third position. The ide switch wipm-r 1'35 and 156 then engage the TH), points 18? and 184 and rhe side switch wiper 130 on gages the contact-point. 131. The side switch mi '2' 135 and 15 thus cxtcml the silliscrilwfe iincccnd actors i554, and by way of thc ccndncturs 185 and =86 and line wipers. 3G and 37, lea -actively. h) the trunk cnminctors 18'? and 1855, as shuwn in Fig. 3. The cngrngcnwn't between said side switch \vipcr I30 and contact-point l; 1, dc scrihml. places a guarding pclemial at the tenth ccntact cf the second level of the privatc bank 41. The connection between said mutant. and ground is as follows: frcm ground G to thc comma-point. Ml, thence to the siilc switch wiper 1250 and ihrcngh the huclcrcicascreluy 4? to thc private Wiper 38 and to the said Contact. The seized trunk-conductors 187 and 188 are thus protected from seizure by other first-selectors which have multiple contacts or terminals of the said seized trunk. At the instant that the said guarding potential is established at the said tenth contact of the second level the vertical switching relay 87" of the two-way trunk switch (I is energized. Said relay receives current from the firstselector A, from the ground (1* to the private wiper HS, lhence to the trunk-release conductor 189, onductor 190, release-armature springs h-l and 125. conductor 191 to the vertical switrhing relay 8T, thence to the battery-h ul 14 and through battery B to ground G. The said relay upon becoming, energized presses the springs 192, 193 and 1 4 into contact, and as a result two operations are simultaneously accomplished, namely a ground connection is established to the vertical triinlt-coiu'luctm' 123 and an energizing urrent is sent through the r0 tary switcl'iing relay 8. The circuit by which the said ground connection is estahlished may he traced from ground G to the springs 194 and 193. thence through the springs l9?) and 1913 of th rotary switcl'iing relay R9" to the springs 197 and 198 of the vertical switching relay 87 to the condiictor 11m and to the vertical trunk-coiuluctor 121 The energizing circuit through the rotary switching relay 8 extends from the same ground U through the springs 194. 19!, and 19:2 to the aid relay R8", thence to the hatter v-leinl 140 and through hattery B to ground (L As soon as the said relay he comes energized it attracts its armature and therehy separates the springs 19?) and 1 0 so that the ground circuit to the vertical tl llll(('( llilll(t(il 12 i. dcscrihed. is at once intcrvuptml. The said momentar' preliminary ground impul e to the vertical trunkconductor 193% causes the vertical magnet 80 of the two-way tlllllh' switch l) at the second exchange to he encrgizcd sullicientl v to die lodge the releas -link from the douhlc dog: luf W). hat not so as to cause the shalt ll of said switch to he raised. The said release-link hcin; dislodged. as descrihed. the armature 2 oi" the relcascanagnet R2 is then moved a little farther from the core of the releasc magnct 2, and asa result the spring Ill-'3 engages the ground sprint i l-" and places a guarding potcntial over the trunk-rcleasc-condactor P29 at all ctm private lilllli contact that are multiplied to said trunlv-rcleascworn du lor. l licrctorc. the seized trunk is not only protected from seizure at the first central cllicc or station. hut at the second central oilirc or station a wcll Not only is a slant electric impulse sent to the \crtical truol conduct-a lit 1 hv thc cn ruization ol' said \crtical and rotary v witching relays 87 and 88 as described, butcertain circuits are changed around as follows: For instance when the vertical switching relay 87 is energized the vertical linerelay 126 that is normally connected to the vertical trunk-conductor 1-33 is disconnected from said tw nk-conductor and connected instead with the vertical lriuik-eonductor 1S7 leading from the first-selector A. The normal connection with the said vertical trunk conductor 123 is from said relay 126 over the conductor 2 .5 to the Co11tact-In iiit i203, side switch wiper 150i. conductor 205, through the vertical switching relay springs 206 and 19S and conductor 199 to the said vertical trunk-conductor 123. The connection between the said vertical line-relay 126 and vertical trunkconductor 187 is from verticai line-relay 126 to the conductor 202, contact-point 203, side switch wiper Q04, and conductor 205 to the spring 20" thence by a new circuit inch-riding the spring 207, conductor 208 to the vertical trunkconductor 13?. Furthermore, when the rotary switching relay R8 is energized the rotary lines-clay 12? in. a similar manner changed from normal connection through the rotary outgoing trunk-(muductor 209 into connection with the local rotary trunk condurtor 188.

The normal ronnetion between the rotary line-relay 127 and the outgoing trunk-conductor 209 may he traced from said rotary linerelay 152? t the conductor i310. thence to the (("ltiH'elNiillll 21L side witch wiper 212, conductor 213 to the rotaryswitching relay springs 2H and 213. conductor 2216 to the outgoing trunk--con luctor 209.. The temporary circuit between vsaid rotary line relay 1;? and the lo al rotary trunk-rouductor 133% may he traced from the said relay 127. over the ame ircuit :lr hel'orc to the spring i l. then to the sp; in; 2l'i'.co1n'luctor 218. and to the local rotary l'l'lllll-( lll(lmlnl 1%. The alling suhscrihcr altcr liming pressed ila hulion l twice and th laitiun ll once presses the liuit m i i twirl: a fil fhlii time. limh time that the said hutton to is press d tlic vcrti -al linca'clzrv [26. nor. leniporarilv connected with the lo al vertical trunk-conductor liv'T. is energized Thc un rcnt l'or cn-r-rglizing said relay llows i'rom ground (1) to the ground post H. thence through spring 1:. to the vertical line-con ductor 1 H. lirst-sclcclo-r side switch wiper 13.1 conta hp inl lh-"i. rondu tor 18.7 to the vertical line-wiper H thence to the aid vertical local trunk-conductor 19?. conductor 2 h. springs 20? and 1200. conductor 203. side switch wiper Jill. contact-point 2 3. con ductor "302 to the said vertical linerclay 12a. thcn c to the hattcrfhlcail lii and through haltcr H to ground (l. llach time that the said vertical line-relay lLfll is cnergized the rlll'll'lflh 2319 and LL' l arc nrcs ed into contact,

- 2m) and thereby one:

and, therefore, the vertical 1ine-relay 84 of the switch 1) is energized also. The energizing circuit for said vertical line-relay 84 extends from ground C through said springs 220 and 219 and through the vertical switching relay springs 19'? and 198 to the vertical trunlecondmrtor 123. The impulse then travels to the second exchange and passes through the vertical switching relay springs 221 and conductor 223 to the side switch wiper 224, thence to the contactpoint 225, corufluctor 228 to the vertical line-relay 84-, thence to battery-lead 140 and through battery 8 to ground G". Since the vertical 5 line-relay 125 of ihe switch C is energized twice, as described, the vertical line-relay 84 of the switch D is also energized twice, and

as result the vertical magnet 80 of the said switch I) is also energized twice, raising the 2; shaft of said switch two steps. Said vertical magnet 8) is energized each time that the vertical lineu'ciay 84 presses the springs 227 and 228 into contact. The energizing cur rent for said vertical magnet- SO may be traced from ground ii through the springs 22?? and Tto the vertical switching relay springs and 221i), thence to the conductor 23.1 and private springs 232 and 233 to the vertical magnet 80, thence through battery So 1% to ground G, Of course, each time that the said vertical magnet 80 is energized the switch-shad 123 is raised one step: and since the an i ringer? is: energized twice the switch-shaft rai is the wipers 134, 235 and.

as 513i to the second level descrihcd in con nection with the firstseiector A) of the line and private banks 225? and 238, respectively. TL-e subscriber having raised the shaft of i ii to the second level, and placed )ere ZE-l and 253 and the private to be rotated into en t c and private banks 2; E and 2 th proceeds to press the rotary button 1 (n for rho second time. As a 46 result the rotary lineu'elay 127 of the switch C i over the following cirs (new zed once cult: from ground it to the ground post 14, hence to the *llllg 13., rotary line-conductor 1:35. roiary side switch i .per 156, con" ij.act{-,ionit iii-i, (.Ol'ldmlni' 125G, rotary lineiripcr EST to the rotary trunkconductor 188, the ice to ti conductor rotary switching relay ogre .217 and 214 to the conductor 2'13. side switch wiper 2122, contacty All and rwcluctor l to the rotary 1 V v 1 H r '7 :uocivlan it;

grows! i, i upon attracting its c ring .5332 into eogag! three h battery B to lined-clay .127 nature ihe it with the spring the rotary linereiav 85, which latter then energizes the private magnet The current for energizing the rotary line-relay of the switch D- flows from grmind (i through the springs 22c and 239 to the conductor 240, thence through the rotary switching relay springs 241 and 215 to the conductor 216, thence to the rotary trunk-conductor 209, conductor 242 at the switch D, rotary switching relay springs 243 and 244, conductor 245, side switch wiper 2 16, contact-point 247, conductor 248, rotary line-relay to the battery-lead 1 10 and through battery 13 to ground G. The rotary line-relay 85 upon attracting its armature presses the s rings" 219 and 228 into contact, whereb a ow of current is sent from ground G t irough the springs 228 and 249, conductor 250, rotary switching relay springs 251 and 252, condoctor 253 to the private magnet -83 (Fig. 30

4), thence to the battery-lead 140 and through battery B to ground G When the private magnet 83 is energized it attracts its armature I18 and operates the side switch F in the same manner that the private mag- 35 net 48 of the first-selector A operates the side switch H, as described. Assuming that the first nine trunks lead ing from the second hank level of the switch 1) are busy the line-Wipers 234 and 235 and the private wiper 236 will be moved, in the manner described in connection with the firstselector A, into engagement with theline bank conductors 254 and 255 and the trunlorelease-conductor 256, as shown in Fig. 4. While the private wiper 236 is passing over busy contacts, of course, the private magnet 83 looks the side switch F insecond position and establishes an energizin circuit through the rotary magnet 81 until the 1t 5 said rotary magnet rotates the shaft 113, as stated. he energizing circuit is from ground 6 to the side switch wiper 256, thence through the rotary magnet 81 to battery B. When the switch I) is thus .oper- 19-5 ated the subscriber's line-conductors 134 and 155' are extended through thefirst-selector A and through the switches C and 1) into connection with the connector E, as shown in F 1 and 2. Therefore, when the pushbutton 10 is pressed twice for the third digit the vertical line-relay 126 of the switch C is. energized twice. As a result .the vertical linerelay 73 of the connector E is ener ized twice. The circuit over which the sai vertical line-relay 73 is energized has already been pointed out and the circuit over which the vertical trunk conductor 123 is grounded when the said relay 126 is operated has also been pointed out. Said ground impulse, as 120 stated, begins at ground G and extends to the vertical trunloconductor 123, then it ex-- tic-a1 iim relay 73 attrarts its armatnrr 260 the springs 261 and 2613 aro pressed into r-nga gonwnt. and as a result the vertical magnet. is energized. The currrnt through the said vertical magnet T flows from ground G through the springs 26; and 261. ionilurtor :MIL private springs :ifi-i and it'iili oou- (lurtor 36H, sillt'} switch wiper 2G7. contartpoint 368 to the vertiral magnrt; T thrnco to tho hattrry-lrml Ht) and through hatter B to ground G. Thi- Yertiral magnet i upon attracting its; armature 2 3 tax i rais the shaft 51" two stops and islarrs tho wiper: v 59 amt fit) opposite the iirat C ntact. f the srronil low} of their l'l'i-titifiVr hanks it and iii The- Sllilt ('1'ilitl operates thirotary tuition 11 again onr'r and thorol y rnrigizcs the rotary iinv-rrtay l2? oi" aha suitrh t owr \i'olhknown rirruits. "hr Stliti win} in urn rausrs tho rotar liiurriay T-t the ronnortor l l to he energized by rurront through a ririrnit a-2 follows: from rounil (i' to thr rotary trunli-roiilu-tor will as prmionsiy liUSi'lil tth thrni o oniiuctor 242 to tho rotary swarm: springs il .itlai ill. comiurtor side swit h whim-134i rontart-point ti 'fl't condor tor 2T0, rotar i line-u ipvr LL rotary trunk conductor J53 to the r iazy lin -rrlay H- and to tho hattervload 'l-l-U, theme through l1atrory Ii to ground ti. "hr "i rotary lin relay upon onrrgrixing prvsws the spring 53k] onto the spring 202 and as a result energizes th" uriratv magnrt T7. 'lho vnvrgixing can rentfthrougli saal private magnvt YT flows from ground ti through the springs 62 and 2.; romlucior -37:. to the priratr mag not 77. thrnro to battery-load Hi anti through hattvry ll to grounil l it The private magnrt '27 upon attrartiug: its armaturv 'I) rausos the tooth fit to vicar thi- PSCEIPQ" .2 rut-linger 27-3. at, \rhirii time thr rillt switch rctrartingrs iring 2U rausvs the said finger 2T3 to engage the tooth "JTT. a ul whon. the armaturo regains its normai position tho said tooth iii in turn i so: .hv finger am! prrmi s tho rfiHi No to draw the sole soiiri. i to si-ronii' iia'ia' ilhll. in \ihi-h osr [ix/ll it is stop a l \i'ir'n tho hag 25TH tho ram $33.

Shifting tilt sizlr wituh to sorontl posh tion auzws tlushio switch ni a r 261' to h-avo thr rontart'point :HH aml ongago in strait tho rontartpoini 137 The result of lliil'i Chango is to Witlhll'tlW tho \rrtii'al magnvt T t'rom tho rontrol ot' the \r-rtiral linurr-lav iii. as dr rrflad. am! to snhstituto thc rota r; magnet T! to tluw-ontrol oi said rvla inatmiih Tho suhsrrihor thou pr rvmis to prrss tho button it) ton timrs tor the last .iigit. whom-or thv vortiral liihx-rolay i of tilt ronm' tor i nvifri ir l ton timos owr rim-nits that haw lawn pointwi out. raiil rrla upon attra ting it: armaturo pro; tho spring-a 71* and Jo; to witter. llach timo that the said springs close into Contact the rotary magnet 71 energized once. The warrant through sairl rotary magnet flows from ground G to the side switch Wiper MT. as in the previous vase. The current then passor to the contact-point 279 and. t0 rim rotary magnet 71. tl'ionco to hatterylead H and through battery 13 to ground I'Iavh time that the rotar magnet 71 is energixrii the shaft :77 rotated one step by the rotary arinaturv Jwt'. in the wolhknown H11 er; ltlitl siurv the subscriber presses the ai wrtical hu tton ten times the shaft; 57 is r tatru' trn steps and the line-Wipers illamt 55 are brought into ronnuotio with tho trnnic imwoniiurtors and 2 3 leading from the: tenth trrminai of the second l ve of the linohani; GE, and the private uipcr it; into mnnection with the private normal ronzhsrtor 233 leading from the tenth ronta-"t oi" the seronil lPvel ot' the pri rats hair i hm the snhscrihor presses tho rotary traitor ii for tho last. timv he again t itf' iivh th rotar'" liue-rciay 12% of the su'itrh t \rhi vh in turn rnorgizos tho l'uitLlW him-relay T1 of tho oonnc or R as bei'oio. The rotary Ura -relay H in turn (HQFglZQz-t tl; a'iiatr magnet '5'? over cir- (aiits that aro known. whereby it operates its armature 273 to permit thr Slti switch I to pass to third position ina \\'a that is ire-ll known. 'hvn tho said. ii'lt'1 switch iiasst's to third position the sulmrrihofs (X- trnilial iinowonitau-tors 54 and '15.; are start-it in ronnm-tion with the normal 00n- (iurtors 281 and as soon as tho side switrh wiprrs 25 i and 28.: rngagc the :ontartpoints 230 and The connection lHtWttH the roniluctor 23 i anti the normal vomlurtor 25- 1 is ostahlishwl through the t nsvr 2 romhrrtor 299 ringer rvlay s n Jigs .OH ami 2:)1. twitli switrh wiper 29h rontart-point 3H3. romlnrtor 129;, wrtiral linvwriprr 5Q to tho \i-rtioai normal coir rtultor 2 The oxti-nilml rotary linrwoir Giulia--25 ronnrrts with the rotarr iormai romhu'tor 2 through tho 'Jnlliltt mi 1923. roinhu'tor :2 ring rr :riay pring 3? am] 3W1 sirlo sa'itrh aipvr 25*157. rontarhpoint 2W. oomiurtor 129T. rotary lim wiprr to tho saiii rotary noi' nai rom urt r \Yhrn thr i=io szvitrh pasx i-s to third position not only antho ralhai iiiwrs ron ilurtors Xtomhal. as tltSi'i'il hut also a guarding potrnt -l is plat-tat at tho it'lllll rontru-t of tho amanul haul of tho [H'iHltP hank il? to pron-rt the shim-ii lino. This ggnaialitng mtuntial is vstahlishwl from tho groom] H" to the rontart'point 2;7. si lo so iti-h \i i wr W1. to tho privato \Yiin'l' HO anti thorn-o to tho tliti ttlltilt't. Saiil guarding mtontiai. t'urthrrmoro. rnorgizrs thr lvriilgcvutotl' rrlay 1'35 oi thr solar-tor A. whi-rrhy thr \rl'tiral :H'il rotary linwroiays '20 and if)! aro rrmonat from across thr normal conductors 981 and 282, for reasons that are obvious) The energizing current in said redo 225 flows from ground G to the private Vibe! 60, conductor 283, through the nor Jimel springs-and winding of the bridge-cut -ofl relay 225, thence to batterydeed 140 'andthrough battery B to ground. G ,Since the normal conductors 281 and 282 land directly to the substation #2220, the

.10 calling subscriber is then in readiness to signal the subscriber at the called substation. If said subscriber should be busy, however, for any reason wliateverthat is, either by reason of being called or by callingthe tenth contact of the second level of the private bank 62 would be conneeted to ground in theWell-lmown way. in such a case the connection would not be com-- as stated, then when the button 11 is pressed some other cmmeetor if the desired the calling subscriber instead of securing "connection with the desired line merely tnergizes the release n'ewnet 72 of the coin hector E When the said button is pressed,

as stated, the rotary linen'chiy 7i ener- 'gized, as previously described, and the pri- "vate magnet 77 is'elso energized as a result. Said private magnet attracts its armature 273 and causes the lateral arm 298 to press the private springs 299 and 306 in. contest and to separate the springs 265 end 266-1. hen the said springs and 300 engage a current then flows from ground to the said private contact in qitiestiou, by way of the fiiSb-Sfilttfl! of the subscriber {if said subscriber is calling}, or by Way of exile scribe/ has hem culled From the said cone tact the current then to the private wiper GO conductor 301, side switclfr wiper 3:72, eontert-poiui 303 conductor 304, private springs 29S? and 30th conductors and 306 to the relrase-nuxgnet 75:2 thence to the hatterpleml H0 and through buttery B to ground if. 7 he releuseznagnet 72 then attracts its ziriniture 39k and thereby restores; the f u-hie dog 3 3% As a result the side switch 5 is re tmfb'fl to normal g'zosition and the switches is :1; f tted to turn to normal position, i v lling Sui-- scriben. thinking he has established connection, presses 21ml mutton and thereby grounds the we! al lllit3-iIFil1flliCtUf 13% over the following path: The ci. from ground G and tinting-h the 'ing}; 18 and -17 to the contact-point ZJl, thence through the spring 32, springs 26 and 27, contactpoint 15 and spring 12 to the vertical lineconductor 134. The result is that the vertical line-relay of the switch 9 is energized, the vertical trunk-conductor 123 is grounded and the vertical line-relay 73 of the connector E is ener ized Said relay, as before, presses the springs 261 and 262 together, and since the side switch I is now in first po sition the vertical magnet *is energized, as has been described i Said vertical magnet then raises the shaft 57 and permits the switch-shaft springs 369 andllt) to come into contact and busy signaling current is sent to the suhscrihefs station, notifvii'ig the subscriber that the felled line is busy. The busy signal current is {generated in the coil 31], shown in l'igi 25, and it then flows iv) the condur-tor 312 to the switchshatt spring 309, thence through the mute spring 310 to the side switch contact-point 3'13, side switch Wiper 285, ringer relay springs 2296 end 295, conductor 25H, condenser 293 conductor wiper of the switch D, oonduetor contact-point 269, side switeh wiper 246. eon ductor i245, rotary switchingrelay springs 24 and 2-1-3, eonductor 5H2, rotary trunlo conductor 20$ condenser 314- of the switch C, conductor Kill, linewiper 36 of the firstselector A, conductor 185, contact-point 183, side switch Wiper 135, vertical lineconductor 134 spring 12 conteotpoint 15, springs; 52? and '36, signaling; hull-1m springs 32; and 33 secen ler v winding 20 of the inilurtioimoil (i receiver iii to the contact point 16, spring 13 rotary lineconductor 155, side switch Wiper 156, and militant-point 1S4, conductor 18%, rotary line-wiper 37, rotary trunkconductor 1R8, condenser 315 Vertical truukconductor123,vertical SWitiflling relay springs 221 and 325: of the snitch Di conductor i223, side switch wiper contact-point 258, conductor 259. vertical line-wiper 234, vertical trunlnconiluctor vertical linorelay T3 to the buttery-lend M0, and back again to the coil 311 The subscriber upon hearing the busy signal will restore his receiver and thereby release all the central oiliee apparatus. When the switch-lmok descends the vertical and r0 tary iinc- 20nductnrs 13% and 15:) are ground ed simnltnimou 'lhi; conneciiox'z lltii' fifi ground and said conrluctm's s from ground G tl'zrough the sprii i8 and 'ii' to the ronductor 332., thence through the releasesprings 39 and to tiurotary line-rm; ductor 1:35 and through the relense springs 30. 2?? and to the ve ti al lineconductor L34. {lronni'i mid ert cal and rotary 2 a ll,

line-coni'luotors snnultnneously energizes the vertical and rotary him-relays 126 and 12? of the switch (I siumltuneanxsl x and said relays in turn reuse the vertical and rotary trunk-remiuctors 13(1209 to he'g'rounded siinultanecuisly, and as a result the vertical and rotary line-relays 73 and 74 f the connector E are also energized simultaneously. The circuits for energizing all of said relays are well-known, since they have already been traced.

'hen the connector line-relays 73 and 74 pull up. as stated, the trunk release springs an; and 317 are pressed into contact. As a result an energizing circuit is: completed through the release-magnet 72 of the conncctor I) in series with the back-release-relay S6 of the switch D. The current flows from ground G at the trunk switch D to the side switch contact-point 31S. side switch wiper 319. conductor 320, back-release-relay 86, conductor 321, private wiper 236, trunk release conductor 256. trunk release springs 316 and 317. conductor 306 to the releasemagnet 72, thence to the batterydead 140* and through battery B to ground G \Vhen the releaseanagnet T2 attracts its armature ill)? the connector-switch is released, as before. but the relays 73 and 74 and the releasemagnet 72 are not deenergized at once. The back-release relay S6 of the trunk switch'l) being energized at the same time that the releascanagm-t 72 is energized presses the springs 3:2 and 2323 into contact, thereby energizing the releaseanagnet S2 of the said switch I). The current through said release-magnet 82 flows from ground (,l and through the springs and 3:23 to the said release-magnet. thence to the battery-lead I'll) and through battery B to ground (lr. \Vhen the said release-magnet 82 attracts its arn'iaturc 93 the release-link 89 is thrust over the lug 90 and at the same time the spring 103 controlled by said release-link witlnlraws from the spring 105 and engages the spring ltll. The said release-magnet stays energized as long as the subscribeus releasesprings remain in con tact. and the switch i not released until the said release-springs disengage. -\Vhen the linc-l'clay 12b and 1'27 of the trunk switch t are energized simultantaiusly the trunk relcase springs 324 and 325 are pressed into contact. thereby placing the release-magnet 32b in series with the hacl\'-release---relay 47 of the first-selector A. \Yhen the backrelcaserclay l7 energizes it closes the bankrchaisc-rclay springs 327 and 328 into contact. establishing an energizing circuit through the release magnet 43. The cur rent in said circuit Hows through ground (1. through the springs 327 and 3L9 to the release-magnet l3. thence to the batterydezn'l Ill) and through battery ll to ground (l. The rclcasc-inagnct l3 ot' the lirst-sclector remains energized after latching the doubl dog 153 in the same manner stated in councction with the trunk switches and D and docs not release the switch until the release-springs at the substation disengage. At the instant that the said releasesprings disengage (when the switclr-luiolt has de scended suflicientlyi the ground circuit to the line-coinluctors v1? and 155 is inter upted and as a result the line-relays lit; and 1:27 of the trunk switch (7 dei nergize. The. ground connection to the illllli condu tors 123 and 201i is rerun-red in turn so that the vertical and rotary llli'.--l'tlu T3 and Tl of the conncctonwwitch al o dci ncrgize. The said connector lincaelayst upon dci nergizing destroy the circuit in which the back-releaserelay 8U of the trunk switch 1) and the relea e-magnet T2 of the connei tor E are in cluded. Said relay and magnet. ot' eourse, will then at once klt'tllt'lEllZtF. The releasemagnet 72 will rcstorc the rclr-ase-armature to normal position. but the hacla-release-re lay 86 (when it permits 1h; springs IL and 323 to separate) dei nei'gizes the releasemagnct 2, at which time the release-arun!-- ture 925 is retracted by the retractlug-spring 92. whereby the double dog id is withdrawn into normal pos tion. However, the release-arniatare til) does not return far enough to separate the springs ll lli and lbs. When the said douhle dog is restored. a stated. the ide switch i and the switchshaft 113 are restored. Not only do the linerelzr s and 1;? of the trunk switch i? remoyc the ground c nnections to the trunlv conductors l2?) and 2W. a stated. but at the, same time. when the springs llil and 335 separate. the circuit thai omprises the release luagnct 126 and thc lan-lt eleasewelay 4? ol the first-selector is broken whereby said magnet and relay are dei nergized. When the baclt-release-relay li pcrmits the springs 312T and 32% to separate the release-magnet 43 is dci nergized. so that the side switch ill and switch shal't 1.3 return to normal posi tion. .\s soon as the private wiper $58 of the first-selector A leares the engaging rinta t tlic micrgizing circuit that has been maintained all along'through the vertical switching relay HT i broken so that said relay is dci nergizcil and rc--torcs the springs under its control to normal position. Of course. as soon as the spring 1912. l9? and 11H- sep arate the energizing circuit through the rotary switching rclny H i in turn broken. whercby the said relay may restore the springs it controls to normal p sition, But it the subscriber is not busy and the connew tion is established. as originally dcscril'icd. then when the subscriber pr his signaling button Ill and grounds he verti al lineconductor lill he energize the vertical linerelay Ti ol the conne tor. as in the last ca-cz but instead of raising th swiich shuft T the ringer rclaw T is energized. since the side with l is in third position and vsince the side switch wipei 313T i in engagcn'ic-nt with the contact-p am 1&1 The current for en ergizing said relay llows from ground (i to the side switch wiper 2G7, tl'icnce through 1 till lit) 323) m the 1 tors, as in the previrms 0115 0, the) iciichvs um uni-ism 1n thv sprin L4 i 252, and aim Lhzzi thv ningrs it and '12.) are mnhu to he Sgl-ilhg WIS mil 104. 3'

same end of such line.

Regardless of which way the automatic trunking is progressing over the twoway trunkline, it is invariably the case that a guarding potential is established at both ends of the said line, whereby the line'is protected against seizure by other subscribers. With this arrangement a subscriber can use the trunk-line for trunking and calling in one direction, and when he does so no subscriber can seize the same line at its other end and attempt to use it in an opposite direction. It will be understood, of course, that when a subscriber seizes one end of a two-way trunk-line no other subscriber can then seize or establishconnection with the The two selectors or trunk-selecting switch mechanisms located at opposite ends of the two-way trunkline are each provided with linerelays adapted to serve also as a portion of the repeating apparatus by which switch operating impulses are repeated from one to another of the inductively connected sections of the line circuit. \Vith this arrangement the vertical line-relay of the combined selector and repeater C is adapted to repeat switch operating impulses into either a local or a line circuit, according to which way the automatic trunking is progressing over the two-way trunk. If the calling is progressing in one direction over the two- "way trunk-line the said vertical line-relay will then repeat'the switch operating impulses from the vertical side of the trunkline to the local circuit including the associated vertical magnet: but it the calling is progressing in the opposite direction. then the said vertical line-relay will repeat switch operating impulses .from the vertical side of 'the subscribers line to the vertical side of the two-way trunk-line. ith such arrangemcnt it is not necessary to-cmploy one or more trunk-lines for trunking and calling in one direction. and one or more trunk-lines for trunking and calling in the opposite direction. \Vith my improved arrangement trunking can be carried on between two automatic exchanges in opposite directions over one and the same trunkdine. For the broader purposes of my invention I. thereforc. do not limit myself to the exact construction shown and described.

it will be seen that the two-way trunkline is provided with means for automatically extending connection therefrom in either direction. and that additional auto matic switching means arc providcd for extending connection to either end of the trunk-line. \Vith this arrangement cach end of the two-way trunk-linc is provided with a set of wipers or line terminals for extending connection therefrom. and each end of the trunk-line is also provided with a set of multiple terminals or bank contacts by which a connection is extended theieto.

It will be understood, of course that the subscribers lines are each provided with a set of wipers or other suitable individual line terminals for extending connection therefrom, and with a set of multiple bank contacts or terminals for extending connection thereto. In this way any subscriber an all any other subscribers telephone line, and if the calling and called telephone lines are located at different exchanges, the connection will then be established over a trunk-line between the same. Subsequently the same trunk-line can then be employed for calling and extending connections in the opposite direction.

In a telephone system of the foregoing character it will be seen that the twoway trunks are each composed of parallel Inetallic conductors. and each trunk is necessarily and invariably used in its entirety that is to say, its (muluctors cannot be used separately in the establishment of any talking circuit or connection. Furthermore. the battery, it will be seen, is normally free from closed circuits in view of the fact that none of the switches have normally closed energizing circuits. and consequently said switches are all normally demagnetizcd. It will also be seen that the ringing of a called subscriber is directly under the control of the calling subscriber. inasmuch as the call ing subscriber must press the ringing key at the calling substation in order to bring about the signaling of the called subscriber. Again. the two-way trunk has an individual switch therefor at each end. and each switch is adapted only for extending connection from the end of the trunk. and its movable linc wipers are operatcd for no other purpose that is. can not be operated to extend connection from the end of any other trunk.

'hat I claim as my invention is:--

l. In a telephone exchange system. the combination of a two-way trunkdinc. automatic switching means for trunking in one dircction over the entire length of said line. and automatic switching means for trunking in the opposite direction over the said linc by automatically establishing connection with the other end thereof. said switching n ans including a switch which is normally dei nergized.

In a telcphonc exchange systcm. the combination of a two-way trunkdinc. subscribers telephone lines. automatic switch ing means for seizing and thereby cxtcnding connection over said trunlclineto a callcd telephone line in one direction. and automatic switching means for seizing and thereby extending connection over said trunklinc to another called telephone line in the opposite direction. said swit hing means llltilll" ing a switch which is normally dccncrgizcd.

3. In a telcphonc exchange system. the combination of a two-way trnnlchne, a nor- ISO line to a called telephone line in one direction, automatic means for extending connection over said trunlcline to another :alled telephone line in the opposite direction. and automatic mcans for establishing a guarding potential for both ends of said trunk-line when the same is used for trunking in either.

combination of a two-way trunk-line, a re peater for u in trunking over said line in one direction. another repeater for trunking over said line in the opposite direction, automatic switches. means for causing said repeaters to transmit switch operating impulses orer said line, and automatic means for establishing a guarding potential for both ends of said trunk-line when the same is nsed for trunking in either direction.

2%). In a telephone exchange system, the combination of a two-way trunk-line. a linen-la at each end of said line, automatic switches controlled by said relay, means for ransinitting switch operating impulses over sad time in one direction. means for transwiiting switch operating impulses over said in the opposite direction, and automatic o ms tor establishing a guarding potential -aboth ends of said trunk-line when the same is used for ranking in either direction. it. In a telephone exchange system, the -z-crnbination of a twoway trunk-line, line-reay at opposite ends of said trunk-line, automal iv switches controlled by said line-relays, mains for using the relays at both ends of tlla trunk-line when the automatic switch i oiwrat l at one end thereof. means for Hing :he relays at both ends of the trunk when the automatic switch is operated the other end thereof. and automatic s ans for establishing a guarding, potential i'- w both ends of said trunk-line when the o is u ed t r trunh ni'r in either direction. 13:? in a telephone ev-hange system, the tion of a thoay trunlcline. a linen o li nd of will trunk-line. an autor 1 '4 ontrolh d by one relay, another :sutom n witrh c ntrolled by the other relay, r In i cali iltff one relay to control the a o no shes. the trunk-line is used for its one dire tion, means for no itii r rt ay to control the said on it no. when the trunk-line is used for M531 K-og; in the op 'te direction. and aut0- 1min Eikt'dll for cstai-lishuig a guarding potential for both ends of said trunk-line when the same is used for trunking in either direction.

23. In a telephone exchange system, the combination of a tw0-way trunk-line, a. pair of line-relays normally bridged across one end of said trunk-line, a pair of line-relays normally bridged across the other end of said trunk-line, an automatic switch c011- trolled by one pair of relays, an automatic switch controlled by the other pair of relays, each automatic switch being provided with means by which it may establish connection from the trunk-line, each end of said trunk-line being provided with means for establishing connection thereto, and automatic means for establishing a guarding potential for both ends of said trunk-line when the same is used for trunking in either direction.

24. In a. telephone exchange system, the combination of a two-way trunk-line, automatic switches for extending connection from either end of said trunk-line. automatic switches for extending connection to either end of said trunk-line, and automatic means for establishing a guarding potential for both ends of said trunk-line when the same is used for trunking in either direction.

2:. In a tclephoneexchange system, the combination of a two-way trunk-line, a set of multiple terminals connected with one end of said trunk-line, a set of multiple terminals connected with the other end of said trunk-line, automatic switches for extending connection to the said trunk-line through the said multiple terminals, means for extending connection from either end of-said trunk-line, and automatic means for establishing a guarding potential for both ends of said trunk-line when the same is used for trunking in either direction.

26. In a telephone exchange system. the combination of a two-way trtlnlcline, auto matic switches for extending connection from either end of said trunk-line. suitable means for extending connection to either end of said trunk line, and automatic means for establishing a guarding potential for both ends of said trunk-line when the same is used for trunking in either direction.

27. In a telephone exchange system. the combination of a two-way trunk-line, auto matic switching machineryfor extending connection from either end of said trunkline, automatic switching machinery for extending connection to either end of said trunk-line, and automatic means for establishing a guarding potential for both ends of said trunk-line when the same is used. for trunking in either direction.

28. In a telephone exchange system, the combination of a two-way trunk-line, automatic trunkselecting switch mechanisms for I es-tul iishingz a gum-ding wad rm iihiiiid! m trunking 3n oppo" dire? and :uitm'nath rm-um a gum-ding potenfla; fur

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trunkextending connection from either end of said trunk-line, automatic trunk-selecting switches for extending connection to either end of said trunk-line, and automatic means for preventing seizure of either end of said trunk-line when the same is used for trunking in either direction.

40. In a telephone exchange system, the combination of a two-way trunk-line, a set of multiple terminals connected with one end of said trunk-line, a set of multiple ter-' minals connected with the other end of said trunk-selecting switches for fitending connection to either end of the said trunk-line mally deenergized automatic "in trunk-line, normally de'energized automatic line, and automatic means for preventing seizure of either end of said trunk-line when the same is used for trunking in either direction.

45. In a telephone exchange system, the combination of a two-way trunk-line, automatic switches, repeaters for transmitting switch operating impulses over said line in either direction, and automatic means for preventing seizure of either end of said trvmkdine when the same is used for trunkin either direction.

6; In a telephone exchange system, the combination of a two-way trunk-line, norswitching through the said multiple terminals, means means for trunking in one direction over for extending connection from either end of said t1 unk-hne, and automatic means for preventing seizure of. either end of said trunkline when the same is used for trunking in either direction.

41. In a telephone exchange system, the combination of a two-way trunk-line, normally dei nergized automatic switches for extending connection from either end. of said trunk-line, suitable means for extending connection to either end of said trunk-line,

said automatic switches common tothe subscribers and individual, to said trunk-line, and automatic means for preventing seizure of either end of said trunk-line when the same is used for trunking in either direction.

42. In a telephone exchange system, the combination of a twoway trunk-line, normally deenergized automatic switching machinery for extending connection from either end of said trunk-line, said switching machinery common to the subscribers, automatic, switching maehiner for extending connection to either end 0 said trunk-line, and automatic means for preventing seizure of either end of said trunk-line when the same is used for trunking in either direction.

4'3. In a telephone exchange system, the combination of a two-way trunk-line, automatic trunk-selecting switch mechanisms for extending connection to either end of said trunkdine, said mechanisms controllable in accordance With a digit of the called number, automatic switch mechanisms common to the subscribers for extending connection from either end of said trunk-line, and automatic means for preventing seizure of either end of said trunk-line when the same is used for trunking in either direction.

44. In a telephone exchange system, the combination of a two-way trunk-line, a pair of relays individual to one end of said line, a pair of relays individual to the other end of said line, automatic means common to the subscribers and controlled by said relays for trunking in opposite directions over said said line, automatic switching means for trunking in the opposite direction over the said'line, another trunk conductor, and a local trunk release circuit at each end of ,said trunk-line, which circuit includes said lastmentioned trunk conductor.

41. In a telephone exchange system, the combination of a two-way trunk-line, sibscritierg to hone lines, automatic switching means or extending connection over said trunk-line to a called telephone line in one direction, automatic switching means for extending connection over said trunkline to another called telephone line in the opposite direction, another trunk conductor and a local trunk release circuit at each end of'said trunk-line, which circuit includes said last-mentioned trunk conductor.

48. In a tgie hone exchange system, the combination yo automatic trunk-selector for automatically trunking over said line in one direction, another automatic trunk-selector for automatically trunking over said line in the opposite direction, another'trunk conductor and a local trunk release circuit at each end of saidtrunk-line, which circuit includes said last-mentioned trunk conductor.

49. In a telephone exchange system, the combination of a two-way trunk-line, a repeater for use in trunking over said line in one direction, anotherrepeater for trunking over' said line in the opposite direction, automatic switches, means for causing said repeaters to transmit switch operating imulses over said line, and a local trunk release circuit at each d of said trunk-line.

50. In a telephon exchange system, the combination of 'QQWp-way trunk-line, a line relay at each end pf said line, automatic. switches controlled by said relays, means for supplying switch operating impulses over said line iii one direction, to energize one of said relays, means for supplying switch-npefiating impulses oversaid line in the ofifisite direction, to energize the other relay, other trunk conductor, and a local trunk release circuit at each end of said a two-way trunk-line, an 

